Optical scanner and image forming apparatus using the same

ABSTRACT

At least one exemplary embodiment is related to an optical scanner, which includes at least one optical element that can separate ghost light from scanning light facilitating the blocking of the ghost light.

FIELD OF THE INVENTION

The present invention relates to an optical scanner and an image formingapparatus using the same. In particular, though not exclusively, thepresent invention relates to an optical scanner suitable for an imageforming apparatus having an electrophotographic process.

DESCRIPTION OF THE RELATED ART

In a conventional optical scanner used in a laser beam printer (LBP) andso on, a light beam that is optically modulated in accordance with animage signal and emitted from a light source device is periodicallydeflected by a light deflector, for example, a rotating polygon mirror.The light beam is converged into a spot on a surface of a photosensitiverecording medium (photosensitive drum) by a scanning optical systemhaving fθ characteristics, and then the surface of the recording mediumis optically scanned to carry out image recording.

FIG. 10 illustrates a schematic view of a conventional optical scanner.

In FIG. 10, a light source device 201 emits a diverging beam. Acollimator lens 203 converts the diverging beam into a substantiallyparallel beam. The beam is limited by a stop 202 and enters acylindrical lens 204, which has a predetermined refractive power only inthe sub-scanning direction. The substantially parallel beam exits thecylindrical lens 204 without being changed in the main scanning section.On the other hand, the beam converges in the sub-scanning section.Therefore, the beam forms a substantially linear image on a deflectingsurface (reflecting surface) 205 a of a deflecting device 205, which isa polygon mirror.

The beam deflected by the deflecting surface 205 a of the deflectingdevice 205 is guided by a scanning lens system 206 having fθcharacteristics, onto a photosensitive drum surface 208 as a surface tobe scanned. The deflecting device 205 rotates in the direction shown byarrow A so that the photosensitive drum surface 208 is optically scannedin the direction shown by arrow B. In this way, image information isrecorded.

In order for such an optical scanner to perform highly accuraterecording of data information, for example, the following conditionsneed to be satisfied:

-   (1) field curvature is reduced throughout the surface to be scanned;-   (2) distortion characteristics between a field angle θ and an image    height Y are fθ characteristics, which enable constant-speed    scanning; and-   (3) the spot diameter on the image plane is uniform at every image    height.

In plastic lenses, a designed aspherical surface can be formed. Inaddition, plastic lenses are inexpensive. Recently, plastic lenses havebeen commonly used in scanning optical systems.

FIGS. 11 and 12 illustrate schematic sectional views showing ghost lightgenerated in a scanning optical system. FIG. 11 illustrates a schematicsectional view in the main scanning direction (main scanning sectionalview). FIG. 12 is a schematic sectional view in the sub-scanningdirection (sub-scanning sectional view).

The scanning optical system 216 is an overfilled scanning opticalsystem, in which the width of an incident beam in the main scanningdirection is larger than the width of a deflecting surface (reflectingsurface) 215 a of a polygon mirror 215. As shown in FIGS. 11 and 12, abeam emitted from a light source device 211 is bent by a returningmirror 217. In the main scanning section, the beam is incident on thepolygon mirror 215 from a direction substantially corresponding to theoptical axis of the scanning optical system 216 (front incidence). Inthe sub-scanning section, the beam is incident on the polygon mirror 215from an oblique direction with respect to a plane perpendicular to therotation axis of the polygon mirror 215 (oblique incidence opticalsystem).

The incident beam Ri travels from the light source device 211 to thepolygon mirror 215. As shown in FIG. 12, when the incident beam Ripasses through part of the scanning optical system 216, it is partlyreflected by a surface 262 a of a scanning lens 262 constituting thescanning optical system 216 to generate ghost light Rf.

Although there are various types of ghost light, this ghost light isso-called stationary ghost light, which can be in the center of theimage independently of deflection angle of the polygon mirror. Thisstationary ghost light stays in the center of the image all the whilethe length of the image is scanned with the real scanning light(scanning beam) Rs. Therefore, although the quantity of the ghost lightitself is small, it is accumulated on the photosensitive drum surface218 and can become larger than the quantity of the real scanning lightRs. The area on which the ghost light Rf is incident is developed into adark line, thereby deteriorating the image quality.

Japanese Utility Model Publication No. 6-35212 discusses an opticalscanner for reducing this ghost light.

In this document, the ghost light problem is reduced by disposing alight blocking member for blocking the ghost light in a position suchthat the light blocking member does not obstruct the incident beam andthe scanning beam.

However, in the case of an optical system in which the ghost light andthe scanning beam are not sufficiently separated, it is difficult tocompletely block the ghost light with the light blocking member.Therefore, other measures can be taken. For example, antireflectioncoating is applied to the surface of the scanning lens.

However, it is difficult to apply antireflection coating to plasticlenses, which are commonly used. In addition, application ofantireflection coating increases the cost.

SUMMARY OF THE INVENTION

At least one exemplary embodiment is directed to an optical scannerincluding a first optical system for guiding a light beam emitted from alight source device (incident beam) to a deflecting device, and a secondoptical system for guiding a light beam deflected by the deflectingdevice (scanning beam) to a surface to be scanned. The incident beampasses through at least one of imaging optical elements constituting thesecond optical system, and is obliquely incident on a deflecting surfaceof the deflecting device in the sub-scanning section. Both the principalray of the incident beam and the principal ray of the scanning beamtravel on one of the upper and lower sides of the optical axis of the atleast one imaging optical element. Both the entrance surface and theexit surface of the at least one imaging optical element are convextoward the deflecting device in the sub-scanning section.

In this exemplary embodiment, both the entrance surface and the exitsurface of the at least one imaging optical element can be concavetoward the deflecting device in the main scanning section.

The light source device can have a plurality of light emitters, and aplurality of light beams emitted from the plurality of light emitterscan be incident on the same deflecting surface of the deflecting device.

The light source device can have two light emitters. In this case, oneof two light beams emitted from the two light emitters can travel on oneof the upper and lower sides of the optical axis of the at least oneimaging optical element, the other light beam can travel on the otherside, and the two light beams can be guided to different planes to bescanned.

In at least one exemplary embodiment, the at least one imaging opticalelement can be tilted in the sub-scanning section.

In at least one exemplary embodiment, the optical scanner can furtherinclude a light blocking member. The light blocking member can bedisposed in the optical path of the second optical system and can blockghost light that is generated by the reflection of the incident beamfrom a surface of the at least one imaging optical element.

In at least one exemplary embodiment, the width of the incident beam inthe main scanning direction can be larger than the width of thedeflecting surface in the main scanning direction.

In yet a further exemplary embodiment, an optical scanner includes afirst optical system for guiding a light beam emitted from a lightsource device (incident beam) to a deflecting device, and a secondoptical system for guiding a light beam deflected by the deflectingdevice (scanning beam) to a surface to be scanned. The incident beampasses through at least one of imaging optical elements constituting thesecond optical system, and is obliquely incident on a deflecting surfaceof the deflecting device in the sub-scanning section. The principal rayof the incident beam travels on one of the upper and lower sides of theoptical axis of the at least one imaging optical element and theprincipal ray of the scanning beam travels on the other side. Both theentrance surface and the exit surface of the at least one imagingoptical element are concave toward the deflecting device in thesub-scanning section.

In yet another exemplary embodiment, both the entrance surface and theexit surface of the at least one imaging optical element can be concavetoward the deflecting device in the main scanning section.

In at least one exemplary embodiment, the at least one imaging opticalelement can be tilted in the sub-scanning section.

In at least one exemplary embodiment, the optical scanner can furtherinclude a light blocking member. The light blocking member can bedisposed in the optical path of the second optical system and can blockghost light that is generated by the reflection of the incident beamfrom a surface of the at least one imaging optical element.

In at least one exemplary embodiment, the width of the incident beam inthe main scanning direction can be larger than the width of thedeflecting surface in the main scanning direction.

In further exemplary embodiments, the optical scanner can beincorporated in an image forming apparatus. The image forming apparatuscan include a photoreceptor disposed on a surface to be scanned. Theoptical scanner can scan the photoreceptor with a light beam to form anelectrostatic latent image. The image forming apparatus can furtherinclude a developer developing the latent image into a toner image, atransferor transferring the developed toner image onto a recordingmedium, and a fuser fusing the transferred toner image to the recordingmedium.

In further exemplary embodiments, the optical scanner can beincorporated in an image forming apparatus. The image forming apparatuscan include a printer controller that converts code data input from anexternal device into an image signal and inputs the image signal intothe optical scanner.

In at least one exemplary embodiment, the optical scanner can beincorporated in a color image forming apparatus. The color image formingapparatus can include a plurality of image carriers that are disposed inplanes to be scanned by the optical scanner and form images in differentcolors.

In at least one exemplary embodiment, the color image forming apparatuscan further include a printer controller that converts color signalsinput from an external device into image data in different colors andinputs the image data into the optical scanner.

When the incident beam passes through at least one scanning opticalelement constituting the scanning optical system, the incident beam ispartly reflected by the surface of the scanning optical element, therebygenerating ghost light. At least one exemplary embodiment reduces ghostlight from being incident on the surface to be scanned, by appropriatelysetting components of the optical scanner. Therefore, the exemplaryembodiment is directed to an optical scanner that can produce ahigher-quality image and an image forming apparatus using the same.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a main scanning sectional view of an optical scanneraccording to exemplary embodiment 1.

FIG. 2 illustrates a sub-scanning sectional view of the optical scanneraccording to exemplary embodiment 1.

FIG. 3 illustrates ghost light in exemplary embodiment 1.

FIGS. 4A and 4B illustrate ghost light generated in comparativeexamples.

FIG. 5 illustrates ghost light generated in another comparative example.

FIG. 6 illustrates a main scanning sectional view of an optical scanneraccording to exemplary embodiment 2.

FIG. 7 illustrates a sub-scanning sectional view of the optical scanneraccording to exemplary embodiment 2.

FIG. 8 illustrates ghost light in exemplary embodiment 2.

FIGS. 9A and 9B illustrate the shapes and angles of lenses incomparative examples.

FIG. 10 illustrates a schematic perspective view of a conventionaloptical scanner.

FIG. 11 illustrates a main scanning sectional view of a conventionaloptical scanner.

FIG. 12 illustrates a sub-scanning sectional view of the conventionaloptical scanner.

FIG. 13 illustrates a sub-scanning sectional view of an image formingapparatus according to an exemplary embodiment.

FIG. 14 illustrates a schematic view of a color image forming apparatusaccording to an exemplary embodiment.

FIG. 15 illustrates a schematic view of another color image formingapparatus according to another exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

The following description of exemplary embodiment(s) is merelyillustrative in nature and is in no way intended to limit the invention,its application, or uses.

Processes, techniques, apparatus, and materials as known by one ofordinary skill in the relevant art may not be discussed in detail butare intended to be part of the enabling description where appropriate.For example member formation and manufacturing may not be discussed indetail; however such processes as known by one of ordinary skill in theart and equivalent methods, processes, and materials would fall withinthe intended scope of exemplary embodiments. For example, materials usedfor and positioning of optical elements (e.g., lens and mirrors) may notbe discussed but materials and positioning techniques as known by one ofordinary skill in the relevant arts is intended to lie within the scopeof exemplary embodiments.

Additionally the actual size of optical elements may not be discussedhowever any size from macro lenses to nano lenses are intended to liewithin the scope of exemplary embodiments (e.g., lenses with diametersof nanometer size, micro size, centimeter size, and meter sizes).

Notice that similar reference numerals and letters refer to similaritems in the following figures, and thus once an item is defined in onefigure, it may not be discussed for following figures.

Exemplary embodiments of the present invention will now be describedwith reference to the drawings.

In exemplary embodiments, imaging optical elements include a refractiveoptical element (e.g., a lens), and a diffractive optical element (e.g.,a lens with a diffraction grating).

Exemplary Embodiment 1

FIG. 1 illustrates a schematic sectional view of an optical scanneraccording to exemplary embodiment 1 in the main scanning direction (mainscanning sectional view). FIG. 2 illustrates a schematic sectional viewof the optical scanner according to exemplary embodiment 1 in thesub-scanning direction (sub-scanning sectional view).

Here, the term “main scanning direction” refers to a directionperpendicular to the rotation axis of the light deflector and theoptical axis of the scanning optical system (a direction in which alight beam is swept by the light deflector). The term “sub-scanningdirection” refers to a direction parallel to the rotation axis of thelight deflector. The term “main scanning section” refers to a plane thatis parallel to the main scanning direction and includes the optical axisof the scanning optical system. The term “sub-scanning section” refersto a plane perpendicular to the main scanning section.

In FIG. 1, reference numeral 1 denotes two light source devices, whichare arrayed vertically (a direction in and out of the paper in FIG. 1)(only the upper one is shown). In the present exemplary embodiment, eachlight source device has a single light emitter. However, exemplaryembodiments are not limited to this. Alternatively, each light sourcedevice may be a multiple semiconductor laser having two or more lightemitters.

Reference numeral 2 denotes a beam converter (e.g., collimator lens),which converts the two light beams emitted from the light source devices1 into substantially parallel light beams (or diverging beams orconverging beams). Reference numeral 3 denotes an aperture stop, whichlimits the beams passing through it to the sub-scanning direction toshape the beams. Reference numeral 4 a denotes a cylindrical lens thathas a predetermined power (refractive power) only in the main scanningsection. Reference numeral 4 b denotes an anamorphic lens that has anegative power in the main scanning section and a positive power in thesub-scanning section. Reference numeral 5 denotes a light deflector(e.g., one having a plurality of deflecting surfaces). In the presentexemplary embodiment, the light deflector can be a rotating polygonmirror having multiple (e.g., ten) surfaces, and is rotated in thedirection shown by arrow A in FIG. 1 at a constant velocity by a drivingdevice (not shown) (e.g., a motor). The cylindrical lens 4 a and theanamorphic lens 4 b make the two collimated light beams formsubstantially linear images on the deflecting surface (reflectingsurface) 5 a of the light deflector 5, in the sub-scanning section.Reference numeral 7 denotes a turning mirror, which reflects the twolight beams toward the light deflector 5.

The collimator lens 2, the aperture stop 3, the cylindrical lens 4 a,the anamorphic lens 4 b, the turning mirror 7, and a first scanning lens61 (as will hereinafter be described) constitute an incident opticalsystem as a first optical system.

In the present exemplary embodiment, two light beams emitted from thelight source devices 1 are made incident on the deflecting surface 5 aof the light deflector 5 by the incident optical system, in the mainscanning section. The width of the incident beams can be larger than thewidth of the deflecting surface 5 a (overfilled optical system). Thespot diameter in the main scanning direction is determined by the focallength in the main scanning direction of a scanning optical system 6 a(as will hereinafter be described) and the area of the deflectingsurface 5 a.

Reference numeral 6 a denotes a scanning optical system (i.e., animaging optical system (fθ lens system)) as a second optical systemhaving a collecting function and fθ characteristics. The imaging opticalsystem 6 a has two (first and second) scanning lenses (fθ lenses) 61 and62 formed of plastic material. The beams based on the image informationare deflected by the light deflector 5 and then form spot images ontheir respective photosensitive drum surfaces 8 (as surfaces to bescanned) through the imaging optical system 6, in the main scanningsection. In addition, the imaging optical system 6 a makes asubstantially optically conjugate relationship between the deflectingsurface 5 a of the light deflector 5 and the photosensitive drumsurfaces 8, in the sub-scanning section. In this way, the imagingoptical system 6 a has a tilt reduction function. In the presentexemplary embodiment, both the entrance surface 61 a and the exitsurface 61 b of the first scanning lens 61 are convex toward the lightdeflector 5.

The present exemplary embodiment has a double path configuration, thatis to say, the two light beams incident on the light deflector 5(incident beams) pass through the first scanning lens (imaging lens) 61,and the two light beams reflected by the light deflector 5 (scanningbeams) enter the first scanning lens 61 again.

In the present exemplary embodiment, when the principal ray of anincident beam travels on one of the upper and lower sides of the opticalaxis of the first scanning lens 61, the principal ray of thecorresponding scanning beam travels on the same side.

Reference numeral 8 denotes photosensitive drum surfaces as surfaces tobe scanned. Each surface 8 is scanned with a spot at a constant speed.

Reference numeral 9 (FIG. 2) denotes a light blocking member havingslits. When the incident beams pass the first scanning lens 61, thebeams are partly reflected by the front surface 61 a or/and the backsurface 61 b of the first scanning lens 61 to generate ghost light. Thelight blocking member 9 reduces ghost light from being incident on thephotosensitive drum surfaces 8.

In the present exemplary embodiment, the two divergent light beamsemitted from the light source devices 1 are converted into substantiallyparallel light beams by the collimator lens 2, are limited by theaperture stop 3, enter the cylindrical lens 4 a, and then enter theanamorphic lens 4 b. The two substantially parallel light beams passthrough the cylindrical lens 4 a and the anamorphic lens 4 b andconverge in the sub-scanning section. The beams are reflected by theturning mirror 7, and then pass through the first scanning lens 61(double path configuration). The beams fall on the deflecting surface 5a of the light deflector 5 and form substantially linear images(extending in the main-scanning direction) near the deflecting surface 5a. At this time, the two beams fall on the deflecting surface 5 a at apredetermined angle (oblique incidence optical system). The two beams inthe main scanning section are limited by the aperture stop 3 withoutbeing changed and then pass through the first scanning lens 61 via theturning mirror 7. The two beams fall on the deflecting surface 5 asubstantially along the center line of the deflection angle of the lightdeflector 5 (front incidence). Where the deflection angle is defined asthe angle the normal of deflecting surface 5 a makes with a planeparallel to the plane of the main scanning section. The width of the twosubstantially parallel light beams is sufficiently large relative to thefacet width of the deflecting surface 5 a of the light deflector 5, inthe main-scanning direction (overfilled optical system).

The two beams reflected and deflected by the deflecting surface 5 a ofthe light deflector 5 form spot images on their respectivephotosensitive drum surfaces 8 through the first scanning lens 61 andthe second scanning lenses (imaging lenses) 62. With the rotation of thelight deflector 5 in the direction shown by arrow A, the beams opticallyscan the photosensitive drum surfaces 8 in the direction shown by arrowB (main scanning direction). In this way, images are recorded on thephotosensitive drum surfaces 8 as recording media.

Table 1 shows numerical values of the optical scanner of the presentexemplary embodiment.

Note that the returning mirror 7 is omitted from Table 1. TABLE 1 angleof oblique incidence in sub-scanning section 1.5 Surface R D N Lightsource 1 1 25.43 1.000 Collimator lens 2 2 ∞ 3.00 1.762 3 −20.635 5.001.000 Aperture stop 3 4 ∞ 18.10 1.000 Cylindrical lens 4a 5 asphericalsurface (see below) 7.00 1.511 6 ∞ 18.10 1.000 Anamorphic lens 4b 7aspherical surface (see below) 3.00 1.524 8 ∞ 193.46 1.000 Firstscanning lens 61 9 reversed shape of surface 13 8.50 1.524 10 reversedshape of surface 12 44.50 1.000 Deflecting surface 5a 11 ∞ 44.50 1.000First scanning lens 61 12 Aspherical surface (see below) 8.50 1.524 13Aspherical surface (see below) 120.50 1.000 Second scanning lens 62 14Aspherical surface (see below) 5.50 1.524 15 Aspherical surface (seebelow) 150.00 1.000 Surface to be scanned 8 16 ∞

Aspherical Shape Surface 5 Surface 7 Surface 12 Surface 13 Surface 14Surface 15 Meridional R 35.993 −9.16E+00 −1.05E+02 −6.06E+01 −1.11E+03 6.14E+04 shape K 0 0  3.04E+00 −3.01E−01 0 −3.87E+04 B4 0 0  6.60E−07 2.61E−07 0 −7.66E−08 B6 0 0 −1.94E−10 −8.85E−11 0  2.82E−12 B8 0 0 5.92E−14 −5.65E−14 0 −7.62E−17 Sagittal r ∞  3.59E+02  1.00E+03 1.00E+03  1.00E+03 −4.41E+01 shape D2 0 0 0 0 0  2.72E−05 D4 0 0 0 0 0−1.91E−09 D6 0 0 0 0 0  1.13E−13 D8 0 0 0 0 0 −2.95E−18

In the present exemplary embodiment, the meridional shapes of theentrance surfaces and the exit surfaces of the first and second scanninglenses are aspherical shapes that can be expressed by functions of up to10th-order. When the intersection between each scanning lens and theoptical axis is an origin, the optical axis direction is the x-axis, anda direction perpendicular to the optical axis in the main scanningsection is the y-axis, the shape in the meridional directioncorresponding to the main scanning direction is expressed by thefollowing formula: $\begin{matrix}{X = {\frac{\frac{Y^{2}}{R}}{1 + \sqrt{1 - {\left( {1 + k} \right)\left( \frac{Y}{R} \right)^{2}}}} + {{B4} \times Y^{4}} + {{B6} \times Y^{6}} + {{B8} \times Y^{8}} + {{B10} \times Y^{10}}}} & \left\lbrack {{Formula}\quad 1} \right\rbrack\end{matrix}$where R is the meridional radius of curvature, and K, B4, B6, B8, andB10 are aspherical coefficients.

The shape in the sagittal direction corresponding to the sub-scanningdirection is expressed by the following formula: $\begin{matrix}{S = \frac{\frac{Y^{2}}{{Rs}^{*}}}{1 + \sqrt{1 - \left( \frac{Z}{{Rs}^{*}} \right)^{2}}}} & \left\lbrack {{Formula}\quad 2} \right\rbrack\end{matrix}$S is the sagittal shape defined in a plane that includes the normal ofthe meridional line in each position in the meridional direction and isperpendicular to the main scanning section.

A radius of curvature in the sub-scanning direction (sagittal radius ofcurvature) Rs at a position that is at a distance of Y from the opticalaxis in the main scanning direction is expressed by the followingformula:Rs*=Rs×(1+D2×Y ² +D4×Y ⁴ +D6×Y ⁶ +D8×Y ⁸ +D10×Y ¹⁰)  [Formula 3]where Rs is the sagittal radius of curvature on the optical axis, andD2, D4, D6, D8, and D10 are sagittal change coefficients.

Although the shape of the surface can be defined by the above formula inthe present exemplary embodiment, other exemplary embodiments are notlimited to this.

In the present exemplary embodiment, in order to achieve such asphericalshapes, both the first and second scanning lenses 61 and 62 can beplastic lenses made by, e.g., injection molding.

In the present exemplary embodiment, as shown in FIG. 2, two beams areemitted from two light emitters (not shown). One of the principal raysof the two light beams travels on the upper side (e.g., 61 c, toward thetop of the page in FIG. 2) and one on the lower (e.g., 61 d, toward thebottom of the page in FIG. 2) side of the optical axis L of the firstscanning lens 61. The two light beams are bent into the main scanningdirection by the common turning mirror 7, pass through the common firstscanning lens 61, and then fall on different positions P1 and P2 on thecommon light deflector 5. The two light beams are deflected by the lightdeflector 5, and then guided to their respective portions on thephotosensitive drum surfaces 8 by the first and second scanning lenses61 and 62.

The light source devices 1 can have various frequencies, thus the twodescribed in the above non-limiting example can have differentfrequencies (i.e., color). Thus for four color scanning two of theoptical scanners illustrated in FIG. 2 can be used to constitute a colorimage forming apparatus that uses four colors C (cyan), M (magenta), Y(yellow), and B (black).

FIG. 3 illustrates an enlarged view of the first scanning lens 61 andits vicinity in FIG. 2. In FIG. 3, the same reference numerals are usedto designate the same components as those in FIG. 2.

In FIG. 3, reference character Ri denotes a beam incident on thedeflecting surface of the light deflector 5 (incident beam). Referencecharacter Rs denotes a beam deflected by the light deflector 5 (scanningbeam). When the incident beam Ri passes through the first scanning lens61, it is partly reflected by the lens surface 61 a to generate ghostlight Rf.

In the present exemplary embodiment, as described above, one of twoincident beams Ri travels on one of the upper and lower sides of theoptical axis L of the first scanning lens 61, and the other travels onthe other side. Since one of the upper and lower incident beams is themirror image of the other (the optical axis L is the line of symmetry),only the upper incident beam Ri is shown in FIG. 3. In the presentexemplary embodiment, as described above, the principal ray of theincident beam Ri and the principal ray of the scanning beam Rs travel onthe same side of the optical axis L of the first scanning lens 61.

Features of at least a few exemplary embodiments will be described usingcomparative examples.

COMPARATIVE EXAMPLES

FIGS. 4A and 4B are sub-scanning sectional views showing comparativeexamples. They illustrate how ghost light is generated when the presentexemplary embodiment is not used. In FIG. 4A, both the entrance surface71 a and the exit surface 71 b of the first scanning lens 71 are flat.In FIG. 4B, both the entrance surface 81 a and the exit surface 81 b ofthe first scanning lens 81 are concave toward the light deflector 5.

In the present exemplary embodiment, as illustrated in FIG. 3, both theentrance surface 61 a and the exit surface 61 b of the first scanninglens 61 are convex toward the light deflector (polygon mirror) 5, andtherefore, compared to the comparative examples (FIGS. 4A and 4B), thedistance between the ghost light Rf and the scanning beam Rs is larger.Therefore, in the present exemplary embodiment, it is possible to ensurea margin between the scanning beam Rs and the light blocking member 9for blocking the ghost light Rf.

FIG. 5 illustrates a sub-scanning sectional view in which the firstscanning lens 71 of FIG. 4A is tilted at a predetermined angle, withrespect to the optical axis L, in the sub-scanning section. In FIG. 5, ascanning beam Rs that travels on the upper side Rsa of the optical axisL is sufficiently apart from its ghost light Rfa. However, a scanningbeam Rs that travels on the lower side Rsb of the optical axis L isclose to its ghost light Rfb.

Therefore, in optical scanners such that one incident beam travels onone of the upper and lower sides of the optical axis L and the otherincident beam travels on the other side as in the present exemplaryembodiment, if the first scanning lens 71 is tilted in the sub-scanningsection, the ghost light Rf and the scanning beam Rs cannot beseparated.

Therefore, in the present exemplary embodiment, both the entrancesurface 61 a and the exit surface 61 b of the first scanning lens 61 areconvex toward the light deflector 5 so that both scanning beams Rs canbe sufficiently separated from their respective ghost light Rf.

In the present exemplary embodiment, the projections of both theentrance surface 61 a and the exit surface 61 b of the first scanninglens 61 onto the plane of the main scanning section are concave towardthe light deflector (polygon mirror) 5 as shown in FIG. 1, therefore,both lens surfaces of the first scanning lens 61 are barrel-shaped.

The smaller the radius of curvature of the first scanning lens 61 in thesub-scanning section, the larger the distance between the ghost light Rfand the scanning beam Rs. However, if the radius of curvature is toosmall, other problems can occur. For example, the spot rotates on thesurface to be scanned.

Therefore, in the present exemplary embodiment, the radius of curvatureof the entrance surface 61 a (r1) and the radius of curvature of theexit surface 61 b (r2) can satisfy the following conditions:

-   -   <r1<10000    -   <r2<10000

In yet another exemplary embodiment, they can satisfy the followingconditions:

-   -   <r1<5000    -   <r2<5000

As described above, the present exemplary embodiment uses two incidentbeams (multi-beam). One of the two beams travels on one of the upper andlower sides of the optical axis L, and the other travels on the otherside in the sub-scanning section. In other words, one incident beamtravels on the opposite side of the optical axis than the side traveledby the other incident beam in the sub-scanning section. However,exemplary embodiments are not limited to this. A single incident beammay be used. In this case, the beam travels on either the upper or lowerside of the optical axis L in the sub-scanning section. In this case,both the entrance surface and the exit surface of the first scanninglens (imaging lens) 61 are convex toward the light deflector 5 as inexemplary embodiment 1. In addition, the first scanning lens 61 istilted in the sub-scanning section so that the ghost light Rf and thescanning beam Rs can be easily separated.

As described above, in the present exemplary embodiment, the ghost lightRf and the scanning beam Rs are apart from each other. Therefore, theghost light Rf can be selectively blocked with the light blocking member9.

The light blocking member 9 can be of various designs (e.g., a metalplate having slits). It is attached to a lens holder for holding thescanning optical system 6. Alternatively, the light blocking member 9may be formed as a unit with a lens holder. Alternatively, the turningmirror 7 may function as the light blocking member 9. In this case, theghost light is reflected toward the light source devices 1 and does notreach the surfaces to be scanned 8. Alternatively, the light blockingmember can be a patterned (e.g., concentric ring) reflective film on theexit side 61 b of the first scanning lens 61, where the initial lightpasses through the center of the pattern but any subsequent ghost lightreflection is blocked by the portion of the reflective pattern having areflective film.

In the present exemplary embodiment, both the entrance surface 61 a andthe exit surface 61 b of the first scanning lens 61 are convex towardthe light deflector 5. However, exemplary embodiments are not limited tothis. Alternatively, at least one exemplary embodiment can have a firstscanning lens 61 such that either the entrance surface or the exitsurface is convex toward the light deflector (polygon mirror) 5.

Exemplary Embodiment 2

FIG. 6 illustrates a schematic sectional view of an optical scanneraccording to exemplary embodiment 2 in the main scanning direction (mainscanning sectional view). FIG. 7 illustrates a schematic sectional viewof the optical scanner according to exemplary embodiment 2 in thesub-scanning direction (sub-scanning sectional view). In FIGS. 6 and 7,the same reference numerals are used to designate the same components asthose in FIGS. 1 and 2.

The present exemplary embodiment differs from exemplary embodiment 1 inthe following respects:

-   (1) the light source device has a single light emitter;-   (2) the scanning optical system 6 b has three (first, second, and    third) scanning lenses 61, 62, and 63;-   (3) the first and second scanning lenses 61 and 62 are formed of a    material with similar optical properties as glass;-   (4) one of the principal rays of the incident beam and the principal    ray of the scanning beam travels on one of the upper and lower side    of the optical axis L of the first and second scanning lenses 61 and    62, and the other travels on the other side in the sub-scanning    section, in other words the incident beam travels on the opposite    side of the optical axis L than the side traveled by scanning beam    in the sub-scanning section;-   (5) the first and second scanning lenses 61 and 62 can be tilted in    the sub-scanning section; and-   (6) the entrance surface 61 a and the exit surface 61 b of the first    scanning lens 61 and the entrance surface 62 a and the exit surface    62 b of the second scanning lens 62 can be concave toward the light    deflector 5 in the sub-scanning section.

Other configuration and optical operations are substantially the same asthose in exemplary embodiment 1.

In FIGS. 6 and 7, reference numeral 19 is a light source device (e.g.,one having a single light emitter). Reference numeral 6 b denotes animaging optical system. The imaging optical system 6 b can have three(first, second, and third) scanning lenses (imaging lenses). The firstand second scanning lenses 61 and 62 are formed of glass or a materialhaving properties similar to glass. The entrance surface 61 a and theexit surface 61 b of the first scanning lens 61 and the entrance surface62 a and the exit surface 62 b of the second scanning lens 62 can beconcave toward the light deflector 5 in the sub-scanning section.

FIG. 8 illustrates an enlarged view of the first and second scanninglenses 61 and 62 and their vicinity in FIG. 7.

In the present exemplary embodiment, one of the principal ray of theincident beam Ri and the principal ray of the scanning beam Rs travelson one of the upper and lower sides of the optical axis L of the firstand second scanning lenses 61 and 62, and the other travels on the otherside. In the present exemplary embodiment, the first and second scanninglenses 61 and 62 can be tilted at an angle β (or at angles β1 and β2,respectively), in the sub-scanning section. The incident beam Ri passesthrough first the second scanning lens 62 then the first scanning lens61. The incident beam Ri is partially reflected by the lens surface 62 bto generate ghost light Rf2. When the incident beam Ri passes throughthe first scanning lens 61, it is also partly reflected by the lenssurface 61 b to generate ghost light Rf1. The tilt of lenses makes theghost light Rf1-2 and the scanning beam Rs distant from each other. Aportion of the ghost light Rf1-2 can be blocked by the light blockingmember 9 and prevented from being incident on a photosensitive drum (notshown).

COMPARATIVE EXAMPLES

FIGS. 9A and 9B illustrate sub-scanning sectional views showingcomparative examples of exemplary embodiments. In FIG. 9A, the entrancesurfaces and the exit surfaces of the first and second scanning lenses71 and 72 are flat. In addition, the first and second scanning lenses 71and 72 are tilted at an angle γ (or at angles γ1 and γ2, respectively),in the sub-scanning section. In FIG. 9B, the entrance surfaces and theexit surfaces of the first and second scanning lenses 81 and 82 areconvex toward the light deflector (polygon mirror) 5. In addition, thefirst and second scanning lenses 81 and 82 are tilted at an angle θ (orat angles θ1 and θ2, respectively), in the sub-scanning section.

The incident beam Ri passes through first the second scanning lens(e.g., 72, 82) then the first scanning lens (e.g., 71, 81). The incidentbeam Ri is partially reflected by the lens surface 72 b or 82 b togenerate ghost light Rf2 a and Rf2 b respectively. When the incidentbeam Ri passes through the first scanning lens (71, 81), it is partlyreflected by the lens surface (71 b, 81 b) to generate ghost light Rf1 aand Rf1 b respectively. As in the present exemplary embodiment, thecomparative examples can also make the ghost light Rf (e.g., Rf1 a, Rf1b, Rf2 a, Rf2 b) and the scanning beam Rs distant from each other.However, flare light incident on the photosensitive drum cannot besufficiently separated from the scanning beam Rs.

Concerning the tilt angle of the first and second scanning lenses in thesub-scanning section, the tilt angle in FIG. 8 (β), the tilt angle inFIG. 9A (γ), and the tilt angle in FIG. 9B (θ) can satisfy the followingcondition:β<γ<θin order to make the ghost light Rf and the scanning beam Rs distantfrom each other as much as in FIG. 8. If the tilt angle is too large,other problems occur. For example, the spot rotates on the surface to bescanned. Therefore, the shape of the first and second scanning lenses 61and 62 shown in FIG. 8 is one possible shape that facilitates a smallertilt angle of the first and second scanning lenses in the sub-scanningsection.

In the present exemplary embodiment, in the main scanning section, theentrance surfaces and the exit surfaces of the first and second scanninglenses 61 and 62 are concave toward the light deflector 5 as shown inFIG. 6, therefore, each lens surface of the first and second scanninglenses 61 and 62 is barrel-shaped.

In the exemplary embodiment illustrated in FIG. 8, the entrance surface61 a and the exit surface 61 b of the first scanning lens 61 and theentrance surface 62 a and the exit surface 62 b of the second scanninglens 62 are concave toward the light deflector (polygon mirror) 5 in thesub-scanning section. However, exemplary embodiments are not limited tothis. Any scanning lens system having at least one lens surface that isconcave toward the light deflector will do.

In at least one exemplary embodiment, both the first and second scanninglenses 61 and 62 are tilted. However, exemplary embodiments are notlimited to this. Alternatively, either the first or second scanning lens61 or 62 may be tilted. As described above, when both the incident beamand the scanning beam pass through a scanning lens, the scanning lenshas a double pass. In at least one exemplary embodiment, both the firstand second scanning lenses 61 and 62 have a double path. However,exemplary embodiments are not limited to this. Alternatively, an imagingoptical system 6 b in which only the first scanning lens 61 has a doublepath will do.

Image Forming Apparatus

FIG. 13 illustrates a schematic sectional view in the sub-scanningdirection, showing an exemplary embodiment of an image formingapparatus. In FIG. 13, reference numeral 104 denotes the image formingapparatus. Into this image forming apparatus 104, code data Dc is inputfrom an external device 117 (e.g., a personal computer). This code dataDc is converted into image data (dot data) Di by a printer controller111 in the apparatus. This image data Di is input into an opticalscanning unit 100 according to exemplary embodiments 1 or 2. Thisoptical scanning unit 100 emits a light beam 103, which is modulatedaccording to the image data Di. With this light beam 103, the opticalscanning unit 100 scans a photosensitive surface of a photosensitivedrum 101 in the main scanning direction.

The photosensitive drum 101, which is an electrostatic-latent-imagecarrier (photoreceptor), is clockwise rotated by a motor 115. With thisrotation, the photosensitive surface of the photosensitive drum 101moves relative to the light beam 103 in the sub-scanning direction,which is perpendicular to the main scanning direction. A charging roller102 is disposed above the photosensitive drum 101, and it is in contactwith the surface of the photosensitive drum 101. The charging roller 102uniformly charges the surface of the photosensitive drum 101. Thesurface of the photosensitive drum 101 charged by the charging roller102 is then scanned by the optical scanning unit 100 with the light beam103.

As described above, the light beam 103 is modulated according to theimage data Di. Irradiation by the light beam 103 forms an electrostaticlatent image on the surface of the photosensitive drum 101. Thiselectrostatic latent image is developed into a toner image by adeveloper 107. The developer 107 is disposed downstream in the rotationdirection of the photosensitive drum 101 from the position irradiatedwith the light beam 103, and it is in contact with the photosensitivedrum 101.

The toner image developed by the developer 107 is transferred onto arecording medium, more specifically a sheet 112 of paper, by atransferring roller 108. The transferring roller 108 is disposed belowthe photosensitive drum 101 and faces the photosensitive drum 101. Thesheets 112 are contained in a sheet cassette 109 in front of thephotosensitive drum 101 (on the right side of FIG. 13). The sheets 112can also be fed manually. A sheet feeding roller 110 is disposed at oneend of the sheet cassette 109, and it feeds the sheets 112 contained inthe sheet cassette 109 into a sheet path.

The toner image is thus transferred onto the sheet 112, and the sheet112 with the unfixed toner image thereon is then carried to a fuserbehind the photosensitive drum 101 (on the left side of FIG. 13). Thefuser includes a fusing roller 113 having a fusing heater (not shown)therein, and a pressing roller 114 pressed against the fusing roller113. The sheet 112 is carried from the transferring roller 108 to thefuser, and the fuser presses and heats the sheet 112 between the fusingroller 113 and the pressing roller 114 so as to fix the unfixed tonerimage to the sheet 112. A sheet-discharging roller 116 is disposedbehind the fusing roller 113. The sheet-discharging roller 116discharges the sheet 112 with the fixed toner image from the imageforming apparatus.

Although not shown in FIG. 13, the printer controller 111 not onlyconverts data as described above, but can also control the motor 115,other units in the image forming apparatus, and a polygon motor in theoptical scanning unit.

The recording density of the image forming apparatus used in exemplaryembodiments is not limited. However, considering that the higher therecording density, the higher the required image quality is, exemplaryembodiments 1 and 2 facilitate the formation of an image formingapparatus that has a recording density of 1200 dpi or more.

Color Image Forming Apparatus

FIGS. 14 and 15 illustrate schematic views of color image formingapparatuses incorporating optical scanners of exemplary embodiments.FIG. 14 shows a tandem-type color image forming apparatus including anarray of two optical scanners of exemplary embodiment 1, the opticalscanners recording image information in parallel on the surfaces ofphotosensitive drums as image carriers. FIG. 15 illustrates atandem-type color image forming apparatus including an array of fouroptical scanners of exemplary embodiment 2, the scanners recording imageinformation in parallel on the surfaces of photosensitive drums as imagecarriers. Reference numeral 60 a denotes the color image formingapparatus illustrated in FIG. 14, while reference numeral 60 b denotesthe color image forming apparatus illustrated in FIG. 15; referencenumerals 11 and 12 denote the optical scanners according to exemplaryembodiment 1; reference numerals 13, 14, 15, and 16 denote the opticalscanners according to exemplary embodiment 2; reference numerals 21, 22,23, and 24 denote the photosensitive drums as image carriers; referencenumerals 31, 32, 33, and 34 denote developers; and reference numeral 51denotes a conveyer belt.

In FIGS. 14 and 15, color signals of R (red), G (green), and B (blue)are input into the color image forming apparatus (e.g., 60 a and 60 b)from an external device 52 (e.g., a personal computer). These colorsignals are converted into image data (dot data) of C (cyan), M(magenta), Y (yellow), and B (black) by a printer controller 53 in theapparatus. These image data are input into the optical scanners 11 and12 (or the optical scanners 13, 14, 15, and 16). These optical scannersemit light beams 41, 42, 43, and 44, which are modulated according tothe image data. The photosensitive surfaces of the photosensitive drums21, 22, 23, and 24 are scanned with the light beams in the main scanningdirection.

The color image forming apparatus of the present exemplary embodimenthas an array of two (or four) optical scanners 11 and 12 (or 13, 14, 15,and 16) corresponding to C (cyan), M (magenta), Y (yellow), and B(black). The optical scanners record image signals (image information)in parallel on the surfaces of the photosensitive drums 21, 22, 23, and24 to print a color image at higher speed than one drum-type color imageforming apparatus of FIG. 13.

In the color image forming apparatus of the present exemplaryembodiment, the two (or four) optical scanners 11 and 12 (or 13, 14, 15,and 16) form latent images of C, M, Y, and B on the surfaces of thecorresponding photosensitive drums 21, 22, 23, and 24 using light beamsbased on the image data. Next, multiple transfer to a recording mediumis performed so as to form a full-color image.

The external device 52 may also be, for example, a color image scanner(e.g., one having a CCD sensor). In this case, the color image scannerand the color image forming apparatus (e.g., 60 a and 60 b) constitute acolor digital photocopier.

In exemplary embodiments the term electrophotographic process caninclude a laser beam printer, a digital photocopier, or a multifunctionprinter, in which a light beam optically modulated and emitted from alight source device is reflected and deflected by a polygon mirror as adeflecting device, and then a surface to be scanned is scanned with thelight beam through a scanning optical system so as to record imageinformation.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures and functions.

This application claims the benefit of Japanese Application No.2004-259913 filed Sep. 7, 2004, which is hereby incorporated byreference herein in its entirety.

1. An optical scanner comprising: a first optical system configured toguide an incident beam emitted from a light source device to adeflecting device; and a second optical system configured to guide ascanning beam to a surface to be scanned, wherein the second opticalsystem includes at least one imaging optical element, wherein theincident beam passes through the at least one imaging optical element,and is obliquely incident on a deflecting surface of the deflectingdevice in a sub-scanning section, wherein both the principal ray of theincident beam and the principal ray of the scanning beam travels on thesame side with respect to the optical axis of the at least one imagingoptical element in a sub-scanning section, and wherein both the entrancesurface and the exit surface of the at least one imaging optical elementare convex toward the deflecting device in the sub-scanning section. 2.The optical scanner according to claim 1, wherein both the entrancesurface and the exit surface of the at least one imaging optical elementare concave toward the deflecting device in the main scanning section.3. The optical scanner according to claim 1, wherein the light sourcedevice has a plurality of light emitters, and a plurality of light beamsemitted from the plurality of light emitters form a plurality ofincident beams on the same deflecting surface of the deflecting device.4. The optical scanner according to claim 3, wherein the light sourcedevice has two light emitters, wherein the two light emitters emit afirst light beam and a second light beam, wherein the first light beamand the second light beam travel on opposite sides of the optical axisof the at least one imaging optical element, and wherein the first andsecond light beams are guided to different surfaces to be scanned.
 5. Anoptical scanner comprising: a first optical system configured to guidean incident beam emitted from a light source device to a deflectingdevice; and a second optical system configured to guide a scanning beamto a surface to be scanned, wherein the second optical system includesat least one imaging optical element, wherein the incident beam passesthrough the at least one imaging optical element, and is obliquelyincident on a deflecting surface of the deflecting device in asub-scanning section, wherein both the principal ray of the incidentbeam and the principal ray of the scanning beam travels on the oppositeside with each other with respect to the optical axis of the at leastone imaging optical element in a sub-scanning section, and wherein boththe entrance surface and the exit surface of the at least one imagingoptical element are concave toward the deflecting device in thesub-scanning section.
 6. The optical scanner according to claim 5,wherein both the entrance surface and the exit surface of the at leastone imaging optical element are concave toward the deflecting device inthe main scanning section.
 7. The optical scanner according to claim 1,wherein the at least one imaging optical element is tilted in thesub-scanning section.
 8. The optical scanner according to claim 5,wherein the at least one imaging optical element is tilted in thesub-scanning section.
 9. The optical scanner according to claim 1,wherein the width of the incident beam in the main scanning direction islarger than the width of the deflecting surface in the main scanningdirection.
 10. The optical scanner according to claim 5, wherein thewidth of the incident beam in the main scanning direction is larger thanthe width of the deflecting surface in the main scanning direction. 11.An image forming apparatus comprising: a photoreceptor disposed on asurface to be scanned; the optical scanner according to claim 1 or 5,the optical scanner scanning the photoreceptor with a light beam to forman electrostatic latent image; a developer developing the latent imageinto a toner image; a transferor transferring the developed toner imageonto a recording medium; and a fuser fusing the transferred toner imageto the recording medium.
 12. An image forming apparatus comprising: theoptical scanner according to claim 1 or 5; and a printer controller thatconverts code data input from an external device into an image signaland inputs the image signal into the optical scanner.
 13. A color imageforming apparatus comprising: the optical scanner according to claim 1or 5; and a plurality of image carriers that are disposed in planes tobe scanned by the optical scanner and form images in different colors.14. The color image forming apparatus according to claim 13 furthercomprising a printer controller that converts color signals input froman external device into image data in different colors and inputs theimage data into the optical scanner.
 15. The optical scanner accordingto claim 1, wherein the at least one imaging optical element is a firstimaging optical element and a second imaging optical element, whereinthe first imaging optical element is tilted a first angle in thesub-scanning section, and wherein the second imaging optical element istilted a second angle in the sub-scanning section.
 16. The opticalscanner according to claim 5, wherein the at least one imaging opticalelement is a first imaging optical element and a second imaging opticalelement, wherein the first imaging optical element is tilted a firstangle in the sub-scanning section, and wherein the second imagingoptical element is tilted a second angle in the sub-scanning section.17. The optical scanner according to claim 15 or 16, wherein the firstangle is not equal to the second angle.
 18. The optical scanneraccording to claim 15, wherein the first and second imaging opticalelements have their respective entrance surfaces and exit surfacesconvex toward the deflecting device in the sub-scanning section.
 19. Theoptical scanner according to claim 16, wherein the first and secondimaging optical elements have their respective entrance surfaces andexit surfaces concave toward the deflecting device in the sub-scanningsection.